THE PLUMULARID.E. 19 



the genus Nematophorus of Clarke (fig. (J9), which is regarded in the present work as a part of 

 Lytwarpux. Dr. (JIarke, in discussing this in conuectiou with yvmutophortiis yrundis, says: 



The cu'uosarc of the most proximal hydrotheca on each pinna iiuds its way to the cicnosarc of the main stem 

 by passing directly through the cavity of the oval basal process, anil from the si/.e of the opening of tho basal process 

 I imagine thai, it must be used for the protrusion of protoplasmic processes like those from an ordinary nemato- 

 phore. Tho process differs, however, from the ordinary uematophores in containing a portion of true civuosarc, and 

 to this extent it approaches tho nature of a, liydrotheca; that is, there exists a swollen, oval process of the perisarc, 

 containing a process of the cienosarc, and with (what in all probability is) a mesial nematophore upon its upper 

 surface. It appears to be, then, a structure which we may look upon as a rudimentary hydrotheca. 1 



Later investigations have demonstrated that the uematophores contain true cu-nosarc, and 

 therefore the above distinction between the hydrauth and uematophores breaks clown. I have 

 carefully examined a number of species exhibiting these processes and found nothing to justify 

 the theory that they are rudimentary hydrotheca'. It appears to mo that the processes themselves 

 contain no cieuosarc, but that the cu* nosarc of the hydrocladium is seen through the aperture 

 of the process, the cavity of which communicates broadly with that of the hydrocladium. Neither 

 have I been able to find the large uematocysts which are so conspicuous in the nematophores of 

 the same species. Jn no case, moreover, have I found the sarcostyle projecting from the orifice. 

 Another feature, which casts a doubt on the theory that we have here to deal with a nematophore, 

 is the fact that in all species which I have examined the usual number of cauliue nematophores is 

 present in addition to the problematical process under consideration. Prof. W. Baldwin Spencer 

 suggests a use for the conical processes which is worthy of consideration. In his discussion of 

 Plumularia procumbent!, he says: 2 



In the axil of the pinnules there are present two nematophores (2) between these a curious structure 



formed of the perisarc, having the shape of a cone with the apex cut off. The space within the latter communicates by 

 the narrow end with the exterior, and by the broader with the cavity of the pinna joint. Into it cells of the ectoderm 

 may enter to a slight degree, but more usually it appears to be unoccupied (in spirit preserved specimens), and I am 

 quite unable to attach any meaning to it, though it is a perfectly constant structure. Possibly it may serve 



as a means of allowing of the ingress and egress of water to and from tlie perisareal tubes. Any space between the 

 ectoderm and the perisarc in the very numerous tubes which compose the colony must presumably be tilled by 

 liquid. The openings leading into the hydrothecie. and uematophores from the stem are small and narrow, and quite 

 filled up by the soft parts. When sudden contraction takes place part of the soft portions must be withdrawn 

 through these openings and occupy space within this perisareal tube previously, presumably, occupied by fluid. If 

 there bo some means of expelling this fluid, then the sudden contraction of the polypes and machopolypes is rendered 

 more easy. It may be that these openings serve this purpose. The openings are guarded, as it were, by two 

 machopolypes. 



The gouosomal uematophores of the Statoplea are quite constant in their general features, the 

 most characteristic form being represented in A. pluma. They are oval in form, borne on the edges 

 of the corbula leaves, and curved so that their apertures are directed nearly upward. They are 

 moiiothalamic, although there is a downward projecting chitiuous process on the interior of the 

 side next the corbula leaf. In the genus Aglaophenla uematophores are borne on both edges of 

 the corbula leaves, although in what is called the "closed" corbula there is apparently but a 

 single row situated on the distal edge of the leaf, those ou the proximal edge being concealed by 

 the imbrication of the leaves. These uematophores vary considerably in size and shape, sometimes 

 assuming the form of a tube (Aglaophenia rathbuni) and again being almost globular (A. pluma). 

 There is often a very long, pointed or tubular nematophore directed forward from near the base of 

 each corbula leaf (.4.. lophocarpa). In the genera possessing phylactogonia the nematophores are 

 arranged in more or less regular rows along the protective brauchlets. Sometimes there is a dis- 

 tinct arrangement in sets of three (Lytocarpus) which are supposed to represent the supracalycine 

 and mesial nematophores of hydrotheca' which have been replaced by gouangia. In several species 

 of Aylaophcnopsis these phylactogonia are jointed, each joint bearing a uematophore oil its outer 

 surface; for example, Aglaophenopsis hirsuta (fig. G5). 



Very long tubular uematophores are found ou the gonosome of Lytocarpus ramosus (Fewkes), 

 and they are further remarkable for having both a terminal and lateral aperture. In Aglaophe- 



1 Report on the Hydroida collected during the Exploration of the Gulf Stream and Gulf of Mexico by Alex- 

 ander Agassiz, 1877-78, Bulletin of the Museum of Comparative Zoology, V, No. 10, p. 249. 



2 A New Family of Hydroidea, together with a Description of the Structure of a New Species of Plumularia, 

 Transactions of the Royal Society of Victoria, 1890, pp. 132, 133. 



